The Second Generation AR57

By Oleg Volk

Introduced around 2010, the AR57 blowback upper receiver for the AR15 uses 50-shot P90 magazines and ejects spent casings down through the nominal magazine well for ambidextrous operation. Operating by simple blowback, this upper is available in 6-inch pistol and 16-inch rifle versions. Chambered in 5.7x28mm, this upper is less powerful than the standard 5.56mm version, but that reduction in power brings certain advantages: reduced muzzle blast, a high practical rate of fire, nonexistent recoil, lightness even when fully loaded and, thanks to the top-mounted magazine, the opportunity for the shooter to get very low to the ground for cover. The upper arrives with a custom buffer that fits any carbine AR15 lower.

The first generation came with a medium-weight fluted barrel and full Picatinny rail, which made the potentially light personal defense weapon into more of a varmint rifle. Unfortunately, the intrinsic accuracy of the cartridge yielded mediocre results for tagging small varmints. Of all available ammunition, RRWS copper hollow-point seems to offer the best combination of accuracy (2MOA) and terminal performance (2/3-inch expansion from the original 0.224-inch diameter and around 15 inches of penetration in gel after four layers of denim). Velocity was around 2680 feet per second with SD under 10, so it was no surprise that this cartridge produced more accurate results than other factory loads.

The second generation cut quite a bit of weight by going to a light profile barrel and M-LOK forend with only small rail segments machined in it top and bottom of the front—ideal for a backup front sight and a bipod. Unloaded, but with a Holosun red dot sight, the 2nd Gen. AR57 on a GWACS Armory polymer lower weighs only 5.3 pounds. Fully loaded, it remains a reasonable 6.7 pounds, light enough for most shooters. Placed on an aluminum lower, it gets slightly heftier but gains length of pull adjustment and more neutral balance.

While the reduction in barrel diameter cuts heat endurance, the cartridge...

This article first appeared in Small Arms Review V21N7 (September 2017)and was posted online on July 21, 2017